13-09-2014, 03:00 PM
MOLETRONICS –
An Invisible
Technology
[attachment=67957]
Abstract
Molecular electronics (moletronics) represent the ultimate challenge in device
miniaturization. The concept of molecular electronics has aroused great
excitement, both in science fiction and among scientists. This is because of the
prospect of size reduction in electronics which is offered by molecular-level
control of properties. Molecular electronics provides means to extend Moore’s
Law beyond the foreseen limits of small-scale conventional silicon integrated
circuits
Introduction
Molecular electronics, also called moletronics, is an interdisciplinary subject that
spans chemistry, physics and materials science. The unifying feature of molecular
electronics is the use of molecular building blocks to fabricate electronic
components, both active (e.g. transistors) and passive (e.g. resistive wires). The
concept of molecular electronics has aroused great excitement, both in science
fiction and among scientists. This is because of the prospect of size reduction in
electronics which is offered by molecular-level control of properties. Molecular
electronics provides means to extend Moore’s Law beyond the foreseen limits of
small-scale conventional silicon integrated circuits.
―Molecular electronics‖ is a poorly defined term. Some authors refer to it
as any molecular-based system, such as a film or a liquid crystalline array. Other
authors, including Tour J. M., prefer to reserve the term ―molecular electronics‖
for single-molecule tasks, such as single molecule-based devices or even single
molecular wires. Due to the broad use of this term, molecular electronics are split
into two related but separate subdisciplines by Petty M. C.: molecular materials
for electronics utilizes the properties of the molecules to affect the bulk properties
of a material, while molecular scale electronics focuses on single-molecule
applications.
Molecular electronics represent the ultimate challenge in device miniaturization.
Molecular devices can have any no of termini with current-voltage responses that
would be expected to be nonlinear due to intermediate barriers or hetero
functionalities in the molecular framework while molecular wires refer to
especially tailored molecular nanostructures energetic properties. Molecular-scale
devices actually operating today include: FETs, junction transistors, diodes, and,
molecular and mechanical switches. Logic gates with voltage gain have been built,
and many techniques have been demonstrated to assemble nanometer wide wires
into large arrays. Programmable and non-volatile devices which hold their state in
a few molecules or in square nanometers of material have been demonstrated.
Advantages of Molecular Electronics
Molecular structures are very important in determining the properties of bulk
materials, especially for application as electronic devices. The intrinsic properties
of existing inorganic electronic materials may not be capable of forming a new
generation of electronic devices envisioned, in terms of feature sizes, operation
speeds and architectures. However, electronics based on organic molecules could
offer the following advantages:
Size – Molecules are in the nanometer scale between 1 and 100 nm. This scale
permits small devices with more efficient heat dissipation and less overall
production cost to be made.
Molecular Electronic Systems
In order to perform as an electronic material, molecules need a set of overlapping
electronic states. These states should connect two or more distant functional points
or groups in the molecule. A conjugated π orbital system is required for a typical
candidate of molecular electronics. This conjugated system needs to extend on an
σ-framework with terminal functional groups. Molecules for electronic
applications generally have 1-, 2-, or 3-dimensional shapes as depicted in Figure .
Alligator clip, which provides stable connection of the material to the metallic
electrodes or inorganic substrates, is the caudal functional group of the organic
electronic material. It is important to note that each part of an organic molecule
used as the active component in nano scale electronic device has their own
contribution. In general, by measuring the conductivity of a series of systematically
modified molecules, the contribution of each component can be determined. For
example, by varying the molecular alligator clip and examining the molecules’
conductivity, the contribution of the alligator clip to the conductivity can be
determined.
Electrode Effects
There has been great interest in molecular electronics since the observation of
electrical conductivity of the molecules from early experiments with the junction
formed by sandwiching the molecule between two metal electrodes. However, it
has been shown that in some systems, it was not the molecules themselves but the
metal contacts that mainly contribute to the junction conductivity. The misleading
observations from early experiments are due to the so called ―metal nanofilaments‖
effect. The ―metal nanofilaments‖ effect is caused by the movements of metal
atoms from the contacts to the tiny gap (several nanometers) between the two
contacts with a bundle of molecules in between when an electric field is applied.
The metal atoms in the gap act as a low resistance bridge between the two contacts.
Instead of flowing through the molecule, electrical current tends to pass through
the low-resistance bridge. More recently, He et al. proposed a metal-free system in
which the two sides of a molecular monolayer attached to single-crystal silicon and
a mat of single-walled carbon nanotubes, respectively Figure .Such a design
eliminated the metal nanofilaments effect and switching property was observed
under an applied field.
Future of Molecular Electronics
The drive toward yet further miniaturization of silicon-based electronics has led to
a revival of efforts to build devices with molecular-scale organic components.
However, the fundamental challenges of realizing a true molecular electronics
technology are daunting. Controlled fabrication within specified tolerances and its
experimental verification are major issues. Self-assembly schemes based on
molecular recognition will be crucial for that task. Ability to measure electrical
properties of organic molecules more accurately and reliably is paramount in future
developments. Fully reproducible measurements of junction conductance are just
beginning to be realized in labs at Purdue, Harvard, Yale, Cornell, Delft, and
Karlsruhe Universities and at the Naval Research Laboratory and other centers.
An Invisible
Technology
[attachment=67957]
Abstract
Molecular electronics (moletronics) represent the ultimate challenge in device
miniaturization. The concept of molecular electronics has aroused great
excitement, both in science fiction and among scientists. This is because of the
prospect of size reduction in electronics which is offered by molecular-level
control of properties. Molecular electronics provides means to extend Moore’s
Law beyond the foreseen limits of small-scale conventional silicon integrated
circuits
Introduction
Molecular electronics, also called moletronics, is an interdisciplinary subject that
spans chemistry, physics and materials science. The unifying feature of molecular
electronics is the use of molecular building blocks to fabricate electronic
components, both active (e.g. transistors) and passive (e.g. resistive wires). The
concept of molecular electronics has aroused great excitement, both in science
fiction and among scientists. This is because of the prospect of size reduction in
electronics which is offered by molecular-level control of properties. Molecular
electronics provides means to extend Moore’s Law beyond the foreseen limits of
small-scale conventional silicon integrated circuits.
―Molecular electronics‖ is a poorly defined term. Some authors refer to it
as any molecular-based system, such as a film or a liquid crystalline array. Other
authors, including Tour J. M., prefer to reserve the term ―molecular electronics‖
for single-molecule tasks, such as single molecule-based devices or even single
molecular wires. Due to the broad use of this term, molecular electronics are split
into two related but separate subdisciplines by Petty M. C.: molecular materials
for electronics utilizes the properties of the molecules to affect the bulk properties
of a material, while molecular scale electronics focuses on single-molecule
applications.
Molecular electronics represent the ultimate challenge in device miniaturization.
Molecular devices can have any no of termini with current-voltage responses that
would be expected to be nonlinear due to intermediate barriers or hetero
functionalities in the molecular framework while molecular wires refer to
especially tailored molecular nanostructures energetic properties. Molecular-scale
devices actually operating today include: FETs, junction transistors, diodes, and,
molecular and mechanical switches. Logic gates with voltage gain have been built,
and many techniques have been demonstrated to assemble nanometer wide wires
into large arrays. Programmable and non-volatile devices which hold their state in
a few molecules or in square nanometers of material have been demonstrated.
Advantages of Molecular Electronics
Molecular structures are very important in determining the properties of bulk
materials, especially for application as electronic devices. The intrinsic properties
of existing inorganic electronic materials may not be capable of forming a new
generation of electronic devices envisioned, in terms of feature sizes, operation
speeds and architectures. However, electronics based on organic molecules could
offer the following advantages:
Size – Molecules are in the nanometer scale between 1 and 100 nm. This scale
permits small devices with more efficient heat dissipation and less overall
production cost to be made.
Molecular Electronic Systems
In order to perform as an electronic material, molecules need a set of overlapping
electronic states. These states should connect two or more distant functional points
or groups in the molecule. A conjugated π orbital system is required for a typical
candidate of molecular electronics. This conjugated system needs to extend on an
σ-framework with terminal functional groups. Molecules for electronic
applications generally have 1-, 2-, or 3-dimensional shapes as depicted in Figure .
Alligator clip, which provides stable connection of the material to the metallic
electrodes or inorganic substrates, is the caudal functional group of the organic
electronic material. It is important to note that each part of an organic molecule
used as the active component in nano scale electronic device has their own
contribution. In general, by measuring the conductivity of a series of systematically
modified molecules, the contribution of each component can be determined. For
example, by varying the molecular alligator clip and examining the molecules’
conductivity, the contribution of the alligator clip to the conductivity can be
determined.
Electrode Effects
There has been great interest in molecular electronics since the observation of
electrical conductivity of the molecules from early experiments with the junction
formed by sandwiching the molecule between two metal electrodes. However, it
has been shown that in some systems, it was not the molecules themselves but the
metal contacts that mainly contribute to the junction conductivity. The misleading
observations from early experiments are due to the so called ―metal nanofilaments‖
effect. The ―metal nanofilaments‖ effect is caused by the movements of metal
atoms from the contacts to the tiny gap (several nanometers) between the two
contacts with a bundle of molecules in between when an electric field is applied.
The metal atoms in the gap act as a low resistance bridge between the two contacts.
Instead of flowing through the molecule, electrical current tends to pass through
the low-resistance bridge. More recently, He et al. proposed a metal-free system in
which the two sides of a molecular monolayer attached to single-crystal silicon and
a mat of single-walled carbon nanotubes, respectively Figure .Such a design
eliminated the metal nanofilaments effect and switching property was observed
under an applied field.
Future of Molecular Electronics
The drive toward yet further miniaturization of silicon-based electronics has led to
a revival of efforts to build devices with molecular-scale organic components.
However, the fundamental challenges of realizing a true molecular electronics
technology are daunting. Controlled fabrication within specified tolerances and its
experimental verification are major issues. Self-assembly schemes based on
molecular recognition will be crucial for that task. Ability to measure electrical
properties of organic molecules more accurately and reliably is paramount in future
developments. Fully reproducible measurements of junction conductance are just
beginning to be realized in labs at Purdue, Harvard, Yale, Cornell, Delft, and
Karlsruhe Universities and at the Naval Research Laboratory and other centers.